The animal core will provide materials (Data Sciences transmitters) and surgical service for instrumentation of rats and mice for chronic measurement of mean arterial pressure, heart rate, and motor activity. Daily care, metabolic data collection, and data acquisition and tabulation from the Data Sciences systems also will be a responsibility of the core, as well as supplemental analyses such as diurnal blood pressure and heart rate variability determinations. Implantation of these animals with osmotic minipumps also will be the responsibility of the core. The core also will provide to all investigators the materials and surgical service for chronic intravenous infusion, repeated arterial blood sampling, and chronic measurement of mean arterial pressure and heart rate in rats. The same computerized data collection and supplemental analyses available for the telemetry studies also will be available for these rats.